Acoustic diaphragm



March 4, 1930. E. c. NILSON ACOUSTIC DIAPHRGM Filed Deo. 16, 1927 RGnZvF-'IGhE FIG, 5

Patented Mar. 4, 1930l UNITED STATES EVEBETT C. NILSON, OF WORCESTER,MASSACHUSETTS, ASSIGNOR OF FORTY PER CENT TO RALPH G. NILSON, OF SANFRANCISCO, CALIFORNIA, AND TWENTY PEE CENT T0 NILS NILSON, OF WORCESTER,MASSACHUSETTS ACOUSTIC DIAPHRAG'MA Application led .December 16, 1927.Serial No. 240,596.

-Ths invention relates to diaphragms of loud speakers of the type knownin the art as cone speakers. Its primary object is to combine theadvantages of the free edge cone and the fixed edge cone and toeliminate some of the faults inherent in each of these types.

A further object of this invention is to devise a' diaphragm having aplurality of aperiodic sections of differing acoustical characteristicswhereby blasting at. any par: ticular sound frequency is eliminated.

A further object is to devise a diaphragm which is unconfned in itsrange and which is responsive to th'e highest notes as well as to thevery lowest notes thereby covering the entire range of audibility.

A further object is to devise a diaphragm which has its center ofinertia approximately at its point of support thereby making the drivingforce more effective at all volumes of received signals and especiallyfeeble signals.

A further object is to devise a diaphragm with a plurality of sectionseach of which is most sensitive to a range of sounds between certainlimiting frequencies.

Another object is to devise effective damping means for each of theseveral sections of which the diaphragm is composed.

Another object is to devise a diaphragm which is more rigid than eithera free edge cone or a fixed edge cone of the same size and material.

Another object is to devise a diaphragm which has light weight but whichis rigid enough over its entire surface to retain its shape whensupported at a single point even when made in enormous sizes.

A further object is to devise a diaphragm which is ornamental anddecorative and Well balanced from an artistic viewpoint.

Further objects and advantages will be readily apparent to those skilledin the art.

Great diiculty has been encountered in attempting to produce a loudspeaker of simple construction which will give faithful reproductionover the entire range 'of audibility. Cone speakers have overcome themain fault of speakers of the horn type, eliminating constriction of thesound waves and interfering echoes. At the present development of theart, however, cone speakers have not been perfected to the extent thatthey will give reproduction without distortion over the entire audiblerange. Due to the fact that every vibrating diaphragm has its own periodof mechanical resonance, sounds of a certain frequency are more readilysustained than sounds of other frequencies and this gives rise todistortion. One method of overcoming this objection is to use adiaphragm which has a natural resonance period outside the audiblerange. When such a diaphragm is used, other disadvantages appear whichare even more objectionable than distortion due to resonance. Forexample, when a diaphragm is used which has a resonant point above theupper limit of audibility, volume of sound is sacrificed on account ofthe small size of such a diaphragm. On the other hand, a diaphragm whichis so large that its natural resonance lies below the musical scale istoo sluggish to respond to the higher notes of the scale unless anunduly strong operating force is applied to it. f-

`This invention overcomes these disadvan tages in a manner which will behereinafter disclosed.

In order that the principles of this invention may be fully understood,attention is called to acompanying drawings in which:

Fig. 1 is a plan view of a dia hragm constructed in accordance with thisinvention.

Fig. 2 is a side view of the diaphragm shown in Fig. 1.

Fig. 3 is a cross section of a modification.

Fig. 4 is a modification having pyramidal sections. --5 I j Fig. 5 is amodification showing the invent-ion applied to a diaphragm of oval orelliptical shape.

Fig. 6 is a modification showing the invention applied to an eccentricdiaphragm.

In Fig. 1 a diaphragm 11 is shown having a central cone 12 with apex 13and circumference 17. Adjacent cone 12 is a truncated cone 14, thesmaller circumference 17Y of which coincides with the circumference ofcone 12. The outer circumference 18 of truncated cone 14 coincides withthe smaller circumference of truncated cone 15 and in a like manner thelarger circumference 19 of the truncated cone 15 is coincident with thesmaller circumference of the truncated cone 16. If desired, moresections, each comprising a truncated cone, may be added to those shownin the illustration. Under some conditions it may also be desirable todispense with some of the sections, so that there may be as few as twosections comprising a central cone and a surrounding truncated cone. Thedimensions of the several sections may be determined from severalstandpoints and I do not wish to be limited to any specific dimensionsor proportions except as defined in the appended claims. Where theacoustical characteristics of the severa-l sections are to be thedeciding factors, more sections or fewer sections may be employed, eachsection being designed to cover its own acousti- Cal range, regardlessof the area of the other sections. The different sections may all havethe same slope or different slopes as conditions may warrant.

In the particular embodiments illustrated, the dimensions and slope ofthe several sections are so chosen that the center of gravity and thecenter of inertia of the diaphragm is approximately at the apex of thecentral I cone 12. It is at this point that the driving force isapplied. It 1s well known that a force applied at the center of inertiaof any mass is far more effective than the same force applied at anyother point and for this reason the diaphragm illustrated will be moreresponsive to forces derived from feeble currents.

Such a construction allows the diaphragm to be supported at any ang-lewithoutdetracting 'from its efciency. This feature is important wherethe diaphragm is large and is suspended at an angle to a wall or otherbackground.

In constructing the diaphragm so that its center of mass occurs at thedriving point, sections lying proximate the driving point ma be of anydesired dimensions, and prefera ly of such dimensions that they mostfaithfully reproduce sounds Within certain frequency ranges and theoutermost section or sections may then be used to balance the diaphragm.The central section 12, for example, may be of such size and mass torespond most faithfully to the highest range of audible sounds, section14 to an intermediate range, and sections 15 and 16 to the lowest rangeand also to balance the diaphragm. It should be remembered, however,that the central section 12 and the other interior sections vibrate inunison with external sections for certain frequency ranges, ashereinafter described, and this should be taken into consideration inselecting the dimensions of these sections. If desired, these sectionsmay be selected in respect to their volume response or any otheracoustic characteristic instead of to frequency response. After thedimensions of the internal section or sections have been fixed, theexterior section or sections of the diaphragm may then be used tobalance the diaphragm so that its center of mass occurs approximately atthe apex of the central section, calculating the dimensions of suchexternal section or sections by means of the formula: i

Where: Q, is the statical moment about an axis passing through the apexof the central section and parallel to the plane of the base of thesection.

M1, M2, M3 M are the masses respectively of the several sections whichcompose the diaphragm.

R1, R2, R3 Rx are the perpendicular dis- ,f

tances of the center of gravity of the sections whose masses are M3, M3,M3 MX respectively, from the axis.

' Since the statical moment about an axis passing through the center ofmass of the diaphragm is equal to zero and since MIR1 and M2R2 may bepredetermined and therefore of known value, the equation under theseconditions becomes:

M3133 MXRX=M1R1M2R2 and where there are but three sections the equationbecomes:

` Males: -MlRfMgla The right hand side of this equation is of knownvalue and any values of M3 and R3 which satisfy the equation willdetermine the dimensions of the outer section which will balance theentire diaphragm so that its center of mass occurs at the apex of thecentral section, at which point the driving force is applied. It will beunderstood that the mass M3 will be different for the differentmaterials of which the section ma be made and the distance R3 will be dierent for different slopes of the section so it is apparent that thereare a number of solutions for the equation.

If desired, the outer section may also be determined by the cut and trymethod, that is, by making it larger or smaller until the diaphragmbecomes balanced at the apex of the central section.

The invention is not limited to a diaphragm ample, will'respond to thehigher notes or sounds because of its relatively small size. There willbe little or no resonance in cone 12 since it is highly damped by theadjacent section 14.

Sounds next lower in the audible range will be reproduced by cone 12candsection 14 vibrating in unison. Resonant vibrations in this range ofsounds are also absent by reason of the damping afforded by the adjacentsection 15. f

Still lower ,sounds will vibrate cone 12, section 14 and section 154 allin unison. Damping is provided for these sections by the section 16.

, Sounds at the extreme lower end of audible range will vibrate thediaphragm as a whole and all sections will be in vibration for suchsounds. Resonance is not important at this stage since the mass of thediaphragm prevents sustaining such resonance.

Since the several sections of the diaphragm are adapted to vibrateindependently to the extent indicated, each section will be damped by anadjacent section which may not be.

vibrating at the same frequency. Damping is extremely effective undersuch circums'tances and the entire absence of resonance in diaphragms ofthis type seems to indicate that the damping thus afforded issubstantially instantaneous in its result. The damping effect providedby the exercise of this invention is in this manner an active force asdistinguished from the passive force applied in certain other dampingarrangements.

It will be obvious that such a construction will produce a diaphragm inwhich more frequencies are reproduced by plunger action of thediaphragm, as distinguished from transverse vibratory waves in thesurface of the diaphragm.- The small central section will act as aplunger type diaphragm on the higher frequencies, while the largersurfaces act as a plunger in reproducing the lower frequencies. By theautomatic allocation of sounds in this manner to surfaces of differentareas, there is a tendency forthe amplitude of vibration `to remain morenearly con-l stant for all of the frequencies provided for in the designof'the diaphragm.'

n speakers of previous design 1t was desirable to use a large diaphragmso that low frequencies might be reproduced without too great a movementof the diaphragm. With such la diaphragm, however, the higherfrequencies were distorted because the diaphragm prevented plunger,action at these frequencies. On the. other hand, when a smallerdiaphragm is' used so that the higher frequencies are more faithfullyreproduced, the lower frequencies cause such a large .amplitude ofvibration that the pole pieces of the electro-magnetic unit arefrequently struck by the diaphragm, thereby setting up Iharsh metallicnoises. ln the dynamic, or

moving coil, type of speaker the metallic noises are eliminated, butthere is a detrimental effect on the iiexibility and elasticity of thedelicate coil supporting spider, thereby destroying its effectivenessand occasionally causing the arms of the support to break because ofmechanical fatigue. Such disadvantages are obviously eliminated by theuse of a diaphragm in which high frequencies are reproduced by a smallarea and the low frequencies by a large area, both having substantiallythe same relatively small amplitude of vibration.

Another important feature of this invention is also due to theindividuality of the several sections and that is the automaticallocation of sounds of different intensities. Feeble forces which aretoo weak to vibra-te the whole mass of the diaphragm will vibrate cone12 alone and the sound will be heard as if a small speaker having a coneof this size were being used. As the intensity of the signals increases,more and more of the sections will come into play and signals which areloud will make use of the whole diaphragm. f

Since feeble forces act upon a relatively small surface and strongforces vibrate a relatively large surface, the amplitude of vibration atthe driving point will tend to remain more nearly constant over theentire volume range thereby giving rise to extremely importantadvantages.

Thus, inI a diaphragm constructed in accordance with the presentinvention, there is a double allocation of the sound emitted from thediaphragm, one determined by the intensity of the sound and the otherdetermined by its frequency, both allocations having a beneficial effecton the performance of the reproducer and increase the amplitude ofvibration under conditions which would otherwise cause the amplitude ofvibration to be too small and decrease it when it would otherwise be toogreat.

Ridges 17 ,.18 and 19 formed at the junctions of the several sectionsmake the structure very rigid and diaphragms may be made in enormoussizes without requiring further support or reenforcement. Thisconstruction does away with the bulky and awkward frame-work required onprevious types of cone speakers of large size. A diaphragm three feet indiameter is very rigid and retains -its shape in any position whenconstructed according to this invention and no further reenforcement ofany kind is'needed. Diaphragms of greater diameter Kthan three feet arealso self-supporting. Smaller diaphragms made in accordance with thisinvention are extremely rugged in` comparison with those of previousdesign.

Another feature of the diaphragm of this invention is that the outersections serve as a baille for sounds emanating from the inner llOrelatively smaller area is provided for the louder sounds, where theneed of a baiile is .less important.

Fig. 3 illustrates a diaphragm of somewhat different appearance. It isreadily seen that an infinite number of shapes and designs may be madewithout departing from the scope of this invention. The dimensions andslopes, either one or both, may be varied giving rise to a wide range ofatterns which are pleasingrto the eye as we l as to the ear. j

ig. 4 illustrates the invention as applied to a diaphragm havingpyramidal sections. What has been explained in regard to a diaphragmcomposed of conical sections applies equally well to the pyramidaldiaphragm.

Various kinds of conical sections may be employed and the invention isnot limited to right circular cones. Elliptical cones, as shown in Fig.5, or oblique cones, as shown in Fig. 6 are examples of some other coneswhich may be used.

Fig. 5 illustrates a diaphragm constructed in accordance with thisinvention having elliptical or oval shape. Such a diaphragm has the sameadvantages over the present oval cones as the circular cone describedhereinblefore has over the simple cone of circular s a e.

ig. 6 illustrates the invention applied to a diaphragm having aneccentric apex.

Many other embodiments of this invention will be apparent to thoseskilled in the art without departing from the spirit of this inventionas defined in the appended claims.

I claim:

1. In a sound amplifying device, a diaphragm, said diaphragm comprisinga cone and a. truncated cone surrounding said cone,

ythe lesser circumference of said truncated cone and the circumferenceof said cone being coincident, the statical moment of said diaphragmabout an axis passing through the apex of said cone and perpendicular tothe axis of said cone bein approximately zero.

2. In a sound amp 'fying device, a diaphragm, said diaphragm bemgcomposed of a plurality of sections said sections comprising a cone anda pluralit of truncated cones, each of said sections a joining anadjacent section along a common circumference, the statical moment ofsaid diaphragm about an axis passing through the apex of said cone andperpendicular to the axis of said cone being approximatel zero.

3. In a sound amplifyin g device, a dia-v phragm, said diaphragmcomprising a cone and a truncated cone surroundin said cone, the lessercircumference of sai truncated cone and the circumference of said conebeing coincident, the center of inertia of said diaphragm being locatedapproximately at the apexcof said cone.

4. In a sound amplifyin device, a diaphragm, said diaphragm bemgcomposed of a plurality of sections, said sections comprising a cone anda plurality of truncated cones, each of said sections adjoining anadjacent section along a common circumference, the center of inertia ofsaid diaphragm being located approximately at the apex of said cone.

5. In a sound amplifying device, a diaphragm, said diaphragm comprisinga cone and a truncated cone surroundin said cone, the lessercircumference of sai truncated cone and the circumference of said conebeing coincident, the center of mass of said diaphragm being locatedapproximately at the apex of said cone.

6. In a sound amplifying device, a diaphragm, said diaphragm beingcomposed of a plurality of sections, said sections comprising a cone anda plurality of truncated cones, each of said sections adjoining anadjacent section along a common circumference, the center of mass ofsaid diaphragm being located approximately at the apex of said cone.

7. In a sound amplifying device, a diaphragm, said diaphragm bemgcomposed of a plurality of sections, said sections comprising a cone anda plurality of truncated cones, each of said sections adjoining anadjacent section along a common circumference, said sections beingindividually designed to have predetermined acoustic characteristics.

8. In a sound amplifying device, a diaphragm, said diaphragm com risinga cone and a truncated cone surroun ing said cone, the lessercircumference of said truncated cone and the circumference of said conebeing coincident, the statical moment of said diaphragm about an axispassing through the apex of said cone and parallel to thebase of saidcone being approximately zero, said cone and truncated cone beingindividually vdesigned to have predetermined acoustic char--acteristics.

9. AIn a sound amplifying device, adiaphragm, said diaphragm belngcomposed of a plurality of sections,'said sections comprising a cone anda pluralit of truncated cones, each of said sections adjoining anadjacent section along a common circumference, the center of inertia ofsaid diaphragm being located approximately at the apex of saidcone andsaid sections being individually designed to have predetermined acousticcharacteristics.

10. In a sound amplifying device, a dia-

